1. Field of the Invention
The present invention relates generally to a specimen moving or manipulating device for an electron beam apparatus. In particular, the present invention concerns a specimen moving apparatus which is capable of moving a specimen disposed on a specimen holder with an improved accuracy while suppressing drifts of the specimen brought about by thermal expansion and contraction of a specimen moving mechanism.
2. Description of the Prior Art
Among electron beam apparatus such as, for example, electron microscopes, there has been known a, one in which a specimen moving device of a so-called side entry type adapted to insert a specimen in the direction perpendicular to the electron beam axis (hereinafter referred to also as optical axis for convenience' sake ) is made use of. A typical specimen moving apparatus of a known structure in which means is provided for protecting the specimen from significant drifts under thermal expansion and contraction of a specimen chamber, objective lens and the specimen moving mechanism brought about by heat generation of the objective lens, variation in the ambient temperature, thermal change of the specimen and the like is illustrated in FIGS. 1 to 5 of the accompanying drawings.
Referring to these figures, a reference numeral 1 denotes a lens column of an electron microscope which defines an electron beam path 30 along the optical axis ( Z-axis ), and a numeral 6 denotes a lower magnetic pole. The lens column 1 and the lower magnetic pole 6 are basic components of the electron microscope. A reference numeral 2 denotes a sleeve-like tilting member having an axial passage 20 and inserted rotatably within a hole formed in the wall of the lens column. The sleeve-like tilting number 2 is so disposed that the axis thereof intersects the optical axis Z. A supporting sleeve 4 provided at a tip end thereof with a spherical portion 3 having a center of rotation A and a bore 21 is disposed rotatably and coaxially within the passage 20. A specimen holder 5 is disposed within the bore 21 of the supporting sleeve 4 so as to be axially movable. The movement or displacement of the specimen holder 5 is restricted by a key 13 anchored in the holder 5 and adapted to engage in a key groove formed in the supporting sleeve 4. The free end portion of the specimen holder 5 ( located on the vacuum side ) is inserted between an upper magnetic pole ( not shown ) and the lower magnetic pole 6. A specimen denoted by a numeral 7 is disposed at a position intersected by the optical axis Z. The supporting sleeve 4 is caused to rotate or swing about the spherical portion 3 by means of a moving or manipulating mechanism composed of an adjusting screw 8 received rotatably in an internally threaded hole formed in the tilting member 2 at a base end portion thereof, a ball 22 and a spring 9 disposed in a recess 16 formed in the tilting member 2 at a position opposite to the screw 8, whereby the specimen 7 is moved horizontally in the direction ( Y-direction ) intersecting orthogonally the axis X of the specimen holder 5 and the optical axis Z.
Further, the supporting sleeve 4 is caused to rotate or pivot about the spherical end portion 3 with the aid of a moving or manipulating mechanism composed of an adjusting screw 10 received rotatably in an internally threaded hole formed in the tilting member 2, a ball 23 and a spring 11 disposed within a recess 17 formed in the inner wall of the tilting member 2 at a position opposite to the screw 10, whereby the specimen 7 can be moved vertically along the optical axis Z.
Through rotation of the tilting member 2, the specimen 7 can be tilted with respect to the X-axis because of corresponding rotations of the spherical end portion 3, the supporting sleeve 4 and the specimen holder 5.
Referring to FIG. 1, the movement of the specimen in the X-direction is accomplished through cooperation of a lever 15 having an arm 27 provided with an acting face at a position located adjacent to the free or tip end of the specimen holder 5 in opposition to the latter, and a coupling member 31 interposed between the lever arm 27 and the tip end of the specimen holder 5, wherein the lever arm 27 and the coupling member 31 cooperate to move the specimen holder 5 in the X-direction. The lever 15 is accommodated within a chamber 14 formed integrally with the lens column 1 of the electron microscope and mounted rotatably on a fulcrum pin 24 so that the lever 15 can be rotated in the X-direction about the fulcrum 24. To this end, an adjusting screw 18 and a spring 19 are provided in association with the other arm of the lever 15, as is best seen in FIG. 1.
The coupling member 31 disposed between the lever arm 27 of the lever 15 and the tip end of the specimen holder 5 is in the form of a spherical cone having a sharp apex 32 and a semi-spherical bottom surface 33, wherein the center of curvature of the bottom surface 33 coincides with the apex 32. The curved bottom surface 33 of the coupling member 31 is brought into contact with the acting face of the lever arm 27 at a point while the apex 32 is so positioned as to bear against the tip end of the specimen holder 5 at a point B, so that the bottom surface 33 may roll on the lateral surface of the lever arm 27 upon rotation of the lever 15 around the fulcrum pin 24. The rotation of the lever 15 in turn is accomplished by means of the adjusting screw 18, resulting in that the lever arm 27 is moved toward or away from the tip end of the specimen holder 5. In this manner, the specimen holder 5 can be moved in the X-direction through the medium of the coupling member 33. Reference numerals 25 and 26 denote O-ring seals disposed, respectively, between the lens column 1 and the supporting sleeve 4 and between the specimen holder 5 and the supporting sleeve 4.
With the specimen moving mechanism of the hitherto known structure described above, the smooth swing movement of the specimen holder 5 for moving the specimen in the Y-direction is accomplished by the coupling member 31 interposed between the lever arm 27 and the specimen holder 5 and having a peculiar configuration such that the coupling member 31 is caused to roll along the lateral surface of the lever arm 27 upon rotation or swing of the lever 15.
This structure however involves various problems in conjunction with the planar movement or vertical movement of the specimen 7. By way of example, it is assumed that the adjusting screw 8 is manipulated to cause the specimen 7 to be moved in the Y-direction to the state shown in FIG. 3. The relationships among the specimen holder 5, the lever 15 and the coupling member 31 in the assumed state are illustrated in some exaggeration in FIG. 4 in the form of a schematic diagram. As will be seen in FIG. 4, the specimen holder is rotated for .alpha. relative to the center of rotation A in accompaniment to the positional adjustment in the Y-direction, while the coupling member 31 rolls along the lever arm 27 to thereby exert an external force F.sub.1 of the horizontal direction from a point C to the center of rotation B located at the tip of the specimen holder 5. This force F.sub.1 is angularly deviated from the specimen holder by the angle .alpha., as shown in FIG. 4. As the consequence, when the adjusting screw 18 is advanced in an effort to move the specimen 7 to the right as viewed in FIG. 3, the tip end of the specimen holder 5 is applied with a force of the direction angularly deviated from the center axis by the angle .alpha.. Consequently, moment of predetermined magnitude acts on the tip end of the specimen holder due to the rotation of the lever 5 and the pressure exerted by the coupling member 31, resulting in that the specimen holder 5 is flexed or deformed about the fulcrum A. Only after the occurrence of such deformation, the specimen 7 is moved in the X-direction (more strictly in the axial direction of the specimen holder 5). Next, it is assumed that the adjusting screw 18 is withdrawn in an effort to move the specimen 7 to the left as viewed in FIG. 3. Then, deformation of the specimen holder 5 brought about by the aforementioned positional adjustment is first removd, and subsequently the specimen 7 is moved in the direction in which the lever 15 is retracted. In this way, a hysteresis phenomenon takes place when the specimen 7 is caused to move in the X-direction on the X-Y plane. This means that the movement of the specimen 7 in the X-direction as caused by manipulation of the adjusting screw 18 and the lever 15 is necessarily accompanied by the movement of the specimen in the Y-direction, making it imposible to position the specimen with accuracy.
It should further be mentioned that the deformation hysteresis of the specimen holder 5 becomes more significant when the lever 15 is rotated counterclockwise for an angle .beta. in addition to the clockwise rotation of the specimen holder 5 for the angle .alpha. relative to the X-axis. In other words, when the specimen holder 5 and the lever 15 are rotated together, an external force F.sub.2 urging the specimen holder and thus the specimen 7 to move in the X-direction gives rise to a remarkable angular deviation .theta. (=.alpha.+.beta.), as will be seen in FIG. 5.